I would say if the marks are in Sharpie then it will be super difficult to remove since the ink is like a stain. Ball point and paint are more superficial and somewhat easier but very time consuming. I have used a waterless hand cleaner with fine pumice and had some success. One thing to remember is the pumice hand cleaner is grinding away at the leather little by little so one needs to be careful. I have applied the cleaner then worked it into the ink with the edge of my fingernail. Success also depends on the type and quality of the leather. Your HOH leather should hold up to the cleaning.

I just checked out Ink-Away on the link and the product description states that it should not be used on unfinished leathers. That applies to just about every baseball glove. I'm sure it works wonders on upholstery leather and shoes, but I'd caution against using it on a glove.